1. Field of the Present Invention
The present invention relates to a semiconductor device, a liquid crystal display device and an electronic appliance. In particular, the present invention relates to a liquid crystal display device and an electronic appliance that control molecular orientation of liquid crystal molecules by generation of an electrical field parallel to a substrate.
2. Description of the Related Art
As for a liquid crystal display device, there are a vertical electrical field type in which an electrical field vertical to a substrate is applied to liquid crystal and a transverse electrical field type in which an electrical field parallel to a substrate is applied to liquid crystal. A liquid crystal display device of a transverse electrical field type is superior in a viewing angle characteristic to that of a vertical electrical field type.
As a method for controlling a gray scale by generating an electrical field parallel to a substrate (transverse electrical field) to move liquid crystal molecules in a plane parallel to the substrate, there are an IPS (In-Plane Switching) mode and an FFS (Fringe-Field Switching) mode.
An IPS liquid crystal display device is provided with two interdigitated electrodes (also referred to as comb teeth-shaped electrodes or comb-shaped electrodes) over one of a pair of substrates. A transverse electrical field is generated by a potential difference between these electrodes (one of interdigitated electrodes is a pixel electrode and the other is a common electrode), which moves liquid crystal molecules in a plane parallel to the substrate.
An FFS liquid crystal display device is provided with a second electrode over one of a pair of substrates, and a first electrode over the second electrode. The first electrode has a slit (opening pattern), and the second electrode has a plate shape (planar shape to cover most slits of the first electrodes). A transverse electrical field is generated by a potential difference between these electrodes (one of the first electrode and the second electrode is a pixel electrode and the other is a common electrode), which moves liquid crystals in a plane parallel to the substrate.
That is, the liquid crystal molecules which are oriented parallel to the substrate (so-called homogeneous orientation) can be controlled in a direction parallel to the substrate; therefore, a viewing angle is increased.
Conventionally, a pixel electrode or a common electrode has been a light-transmissive conductive film; therefore, it has been formed of ITO (indium tin oxide) (Patent Document 1: Japanese Published Patent Application No. 2000-89255).